1. Field of the Invention
The present invention relates to a miniature push switch packaged on a substrate to be turned on/off by the reversing action of a belleville spring, and a method of producing the same.
2. Description of the Related Art
It is desirable that a push switch packaged on a substrate is small in size and low in cost, and at the same time, have an accurate contact condition, a high operability and durability. To meet these requirements, a conventional push switch, as shown in FIG. 24, comprises a central contact 202 and a peripheral contact 203 making up a conducting circuit securely fixed to an insulating case 201, and a belleville spring 204 upwardly covex in contact with the peripheral contact 203 along the outer edges thereof. Further, such a push switch comprises an actuator 205 formed with a protrusion 205a in contact with the top of the belleville spring 204. When the actuator 205 is pressed from the upside, the protrusion 205a pushes the belleville spring 204 downwardly, so that the interior surface of the central part of the belleville spring 204 comes into contact with the central contact 202. As a result, the central contact 202 is electrically connected to the peripheral contact 203 through the belleville spring 204.
In a conventional method of fabricating the above-described push switch, as for example disclosed in JP-B-56-43573, a multiplicity of conducting circuits, each including a pair of central and peripheral contacts, are coupled in a sequence, and a multiplicity of mounts for holding the conducting circuits are insert-molded, after which a push spring (belleville spring) is placed in a recess of each mount.
In this conventional push switch, the belleville spring is movable horizontally in a case or mount, and it is impossible to maintain secure contact with the peripheral contact. Also, for the same reason, the peripheral contact is exposed to the atmosphere, often causing a contact failure due to intrusion of dust, etc. Further, if the push switch is washed with water after being packaged in the substrate, moisture penetrates, thereby hampering automation of the work of substrate assembly. If the thickness of the belleville spring is increased in order to improve the sensitivity of the operation of the switch, the internal stress required for elastic deformation is increased, with the result that the push switch is easily damaged by repetitive fatigue, thereby leading to a lower durability. In addition, it is necessary to mount the belleville spring, an operating button for pushing down the spring and a cover serving as a protective member in different processes, thus complicating the fabrication processes.